1. Field of the Invention
The present invention relates to external fluid flow across a foil, such as an airfoil or hydrofoil, and particularly, to a method and system for influencing and regulating the properties and characteristics of the fluid flow, and thus the fluid flow itself, across the surface of an airfoil or hydrofoil, such as a propeller, a turbine or turbine blade, a fan blade, an impeller, a blower, and others, which, in effect, optimizes the fluid flow, thus increasing the efficiency of the foil, as well as the actual properties and characteristics of the fluid.
2. Background of the Invention and Related Art
As an object moves through a fluid, or as a fluid moves over the surface of an object, the molecules of the fluid near the object become disturbed and begin to move about the object. As the fluid continues to move over the object's surface, those molecules adjacent the surface of the object have the effect of adhering to the surface, thus creating negative forces caused by the collision of these molecules with other molecules moving in the free stream. The magnitude of these forces largely depends on the shape of the object, the velocity of fluid flow with respect to the object, the mass of the object, the viscosity of the fluid, and the compressibility of the fluid. The closer the molecules are to the object, the more collisions they have. This effect creates a thin layer of fluid near the surface in which velocity changes from zero at the surface to the free stream value away from the surface. This is commonly referred to as the boundary layer because it occurs on the boundary of the fluid. The collision of molecules at the surface of an object creates inefficient and unpredictable fluid flow, such as drag, and inevitably turbulence and vortexes.
Most things in nature try to exist within a state of equilibrium. The same is true for fluid flow over the surface of objects found in natural environments. For example, during a wind storm over the dessert, or a snow storm over a field, or even the sand on the beach as the water flows over and over, evidence exists that a state of equilibrium between the fluid flow and the surface over which the fluid is flowing is trying to be reached. As conditions are not perfect and the flow must be less than completely laminar, the surface of these natural conditions forms several sequential ripples or ledges that indicate the fluid and the surface are reaching as close a state of equilibrium as possible. Just like in nature, manufactured conditions and situations are equally not able to reach perfect conditions of fluid flow.
The study of aerodynamics over a surface has been extensive. However, over the years, the prevailing theory or idea has been that smoother or streamlined is better and operates to optimize fluid flow. As such, every conceivable manufactured device or system in which fluid passes over the surface of an object has been formed with the surface being as smooth and streamlined as possible.
The fields of fluid dynamics and aerodynamics study the flow of fluid or gas in a variety of conditions. Traditionally this field has attempted to explain and develop parameters to predict viscous material's behavior using simple gradient modeling. These models have enjoyed only limited success because of the complex nature of flow. Low velocity flow is easily modeled using common and intuitive techniques, but once the flow rate of a fluid or gas increases past a threshold, the flow becomes unpredictable and chaotic, due to turbulence caused by the interaction between the flowing material and the flow vessel. This turbulence causes major reductions in flow rate and efficiency because the flow must overcome a multi-directional forces caused by the turbulent fluid flow.
Attempts to improve flow rate and efficiency, scientists and engineers have traditionally accepted the principle that the smoother the surface the material is passing over, the lower the amount of turbulence. Thus efforts by scientists and engineers to improve flow and efficiency rates have generally focused on minimizing the size of the surface features across which the material is flowing. Because the turbulence is caused by micro-sized surface features, efforts to minimize these them have always been limited by the technology used to access the micro-sized world.
Turbulence occurs at the rigid body/fluid or gas interface also know as the boundary layer. The flowing material behaves predictably i.e. in a laminar fashion, as long as the pressure down flow remains lower than the pressure up flow. Generally as the rate of flow increases the pressure also increases, and the pressure gradient in the boundary layer becomes smaller. After a certain threshold is achieved, the flow closer to the rigid body is much slower than the flow outside the boundary layer, thus the pressure directly in the orthogonal direction from the rigid body is less than the pressure down flow. This causes the kinetic energy of the molecules in the boundary layer to move in the direction of the lowest pressure, or away from the rigid body. This change in the direction of the material, from moving in the direction of flow to moving across the direction of flow in the boundary layer creates vortices within the boundary layer and along the rigid body. These vortices create drag because the direction of flow as well as the kinetic energy of the particles is not in the down flow direction alone, but in a variety of directions. As a result, large amounts of energy are required to overcome the drag force, lowering the flow rate and efficiency.
Developments in the past few decades have improved on the traditional understanding of flow over a rigid body, resulting in advances in mathematical and computer modeling, as well as improved theoretical understanding of a material's behavior under non-ideal circumstances. Most of these advances have focused on improving the flow surface.
One such example of an improved flow surface is to use a rough flow surface that creates myriad miro-vortices much like a shark's skin or sand paper. It is thought that these small turbulence zones inhibit the creation of larger and more drag creating vortices. While these rough materials have been used in advanced racing yacht hulls as well as in swimming suite materials, there is still not a large improvement over smooth surfaces. Thus the state of the art is still struggling to understand turbulent flow beyond specific equations, and applications are still slowed by the drag and inefficiency caused by the turbulent flow.